I got several requests for a VCO like I have in my JH-5, something that doesn't have the focus on precision but on character, with "linear detuning", and some of that early Moog and EMS character (without being a clone):
http://jhaible.heim.at/jh5/jh5.html

The main reason why I hesitated so long was as simple as it was embarrassing: I couln't find my design documents - I must have lost them in moving houses some years ago. The prospect was that'd I'd have to reverse-engineer my own prototype if I wanted to offer a PCB for this ...

But some days ago, I found my PSpice simulation files, which show the main parts of the VCO and VCO driver circuits in a form that must be very close to what I've actually built in the JH-5.

So, suddenly the possibility is there ...

JH._________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)Last edited by jhaible on Wed Dec 10, 2008 4:13 pm; edited 1 time in total

At the moment, we're just talking about a possibility.
I don't have any specific plans yet.

JH._________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

Wow - great news! I'd be up for doing several. I have been planning on doing the "linear detune SEM VCO mod" (from Roy Tate's website) on a couple of MOTM 310's (since they're basically the same topology), but this would be better

I have a design question concerning this constant Hz offset that I think is very interesting. I know the schematic you designed for the SEM VCO using an extra cap in series with the VCO timing capacitor.

If say the VCO has a classical servo OPAmp exponential current converter, could it be that by simply adding an offfset voltage on the lin FM input of the servo circuit (the inverting input of the OPA) one could get the same effect or is there an obvious difference with what you proposed ?

I have a design question concerning this constant Hz offset that I think is very interesting. I know the schematic you designed for the SEM VCO using an extra cap in series with the VCO timing capacitor.

If say the VCO has a classical servo OPAmp exponential current converter, could it be that by simply adding an offfset voltage on the lin FM input of the servo circuit (the inverting input of the OPA) one could get the same effect or is there an obvious difference with what you proposed ?

Thanks in advance

Yves

Yes, there's a difference.
(And the new implementation isn't like that SEM modification either.)

JH._________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

Yes, there's a difference.
(And the new implementation isn't like that SEM modification either.)

I am even more intrigued !
Can you tell us what is the benefit of your design compared to what I was referring to in my previous message ? I am definitely interested...
:

I don't think that a voltage offset in the servo loop causes what I mean with linear detuning. (I think it causes linear FM.)

I should have found a better word for what I mean, many years ago, I know.
"Linear" refers to the behaviour of Linear (V/Hz) VCOs, not to linear FM in exponential VCOs.

JH._________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

"Linear" refers to the behaviour of Linear (V/Hz) VCOs, not to linear FM in exponential VCOs.

Hi again Jurgen,

Pardon my ignorance but checking the MS20 VCO which operates as a linear V/Hz VCO, the keyboard CV and V/Hz input is directed to that very point (inverting input of IC3) ? I'd conclude that using a voltage offset would create a constant Hz offset, wouldn't I ? Do I misunderstand something ?

[EDIT] Ok I think I get the difference, the V/OCT input somehow modifies the range of offset from the linear modulation, the modulation stays linear but its extents is modified by the V/OCT input. And say if I increase from 1V on the V/OCT input this will double the range of the linear modulation... Thus a constant offset on the linear input will not result in a constant frequency offset if I apply 1V on the V/OCT input. Am I right ?
[/EDIT]_________________YvesLast edited by yusynth on Wed Dec 10, 2008 5:59 am; edited 2 times in total

The only other solution I foresee is to have a second current source/sink to feed the timing cap. This second source (or sink) being linearly controlled by an offset voltage. Thus the time cap receives the sum of the currents from the expo converter and from the linear current source.

The only other solution I foresee is to have a second current source/sink to feed the timing cap. This second source (or sink) being linearly controlled by an offset voltage. Thus the time cap receives the sum of the currents from the expo converter and from the linear current source.

Is it something like that ?

Yves

JH._________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

That's a good question.
Depends on how many waveforms you need.
In the JH-5, there's only saw and pulse (with PWM) and one Oscillator Driver controlling 3 VCO cores. This can be very compact. Maybe (maybe!) 3 VCOs on a single 27 Euro PCB.
If you want full fledged VCOs with all waveforms and all kind of modulation inputs, it's probably one VCO per board.

Is there a way to add a poll on a thread that's already in use?

JH._________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot vote in polls in this forumYou cannot attach files in this forumYou can download files in this forum

Please support our site. If you click through and buy from our affiliate partners, we earn a small commission.